A critical study of the conditions and limits of conditions for the linear response of dual wavelength split beam spectrophotometers has been completed. With this information, our newly developed system for electrodic potentiometry was applied to a study of the respiratory chain of E. coli. Computer modeling was used to identify the spectral components present in a membrane suspension in the presence of six redox mediators. This approach has yielded much new information about the redox components present in E. coli membranes.